I dont know if RM use Avonride axles - but I have a cross reference for most bearing manufacturers with part numbers for both X and Y series ......
PM if you want as I cannot attach a word doc to this post.
You can get them from most bearing suppliers or from car spares/motor factors. If you have the old bearing part number google it and you may find a site that lists equivalents. These are a cheaper source than even TrailerTek or Western Towing whom I had used before. The nuts are definitely worth getting though..... also check that the bearings from a motor factor come with two circlips as some dont and you need them.
You may need a press to actually get them out .... and use the old carrier to to push the new ones in. As others say, do not put pressure on the inner.
.... sealed for life
I change mine every two years